January 5, 2009

Yellowstone Tremors Subside For Now

The nearly 300 small earthquakes that have rumbled underneath Yellowstone National Park during the past week seem to have subsided for now, according to data from the Yellowstone Volcano Observatory.

The swarm of small earthquakes, the largest in more than two decades, began during the last week of December, and include three quakes that happened last Friday -- a magnitude 3.5 quake at 11:30 a.m., followed by quakes measuring 3.2 and 3.1 at 12:40 p.m. and 1:15 p.m.

Scientists and emergency authorities are continuing to closely monitor the activity.

The hundreds of quakes are all centered under the north end of Yellowstone Lake. The strongest quake was a magnitude 3.9 quake that occurred last Saturday.

No damage has yet been reported, and the park's alert status remains at Green at this time. Since the park's central area is accessible only by snowmobile this time of year, few were present to actually feel the tremors.

Yellowstone National Park sits atop a supervolcano. In fact, the entire park is the depression of a vast caldera that is the result of an enormously large eruption that took place about 600,000 years ago. But even today the park remains very geologically active. Indeed, Yellowstone's hot springs and geysers are a reminder that a pool of magma still exists five to 10 miles underground.

Scientists studying Yellowstone from the U.S. Geological Survey, University of Utah and National Park Service at the Yellowstone Volcano Observatory say recurrences of cataclysmic eruptions are not predictable.

Geological records document eight known supervolcanic eruptions, but there may have been more. To be sure, a supervolcano eruption at some point in the future is inevitable.

However, the researchers said that while Yellowstone erupts about every 600,000 years, nothing, including the recent tremors, conclusively indicates an imminent eruption.

Other scientists are also doubtful on whether or not the quakes point to an upcoming major seismic event.

"It could be, but the swarming is too "isolated", i.e., it is near the lake area only," said volcanologist Dr. R.B. Trombley of the International Volcano Research Centre in an interview with US News & World Report.

"Much greater magnitude earthquakes, over a larger area of the caldera," would be needed to signify a major volcanic event, he said.

"The caldera is approx. 32 mi long by 8 miles wide. I believe the greatest quake so far has only been a 3.9 and all of the 'quakes so far have been from 1 to 10 km of depth."